The present invention relates to a new block copolymer.
The living polymerization is useful for the production of monodisperse polymers and block copolymers of uniform composition, and many attempts have been made for the production of olefin block copolymers by living polymerization also in the area of coordinate polymerization that employs a Ziegler-Natta catalyst. However, it is difficult to produce block copolymers of uniform composition by living polymerization because chain transfer reactions and termination reactions take place frequently during living polymerization.
The present inventors found that a catalyst composed of V(acetylacetonate).sub.3 and Al(C.sub.2 H.sub.5).sub.2 Cl provides nearly monodisperse living polypropylene. [Makromol. Chem., 180, 1359 (1979); and Makromolecules., 12, 814 (1979)] The present inventors also found that this technology can be applied to the living copolymerization of ethylene and propylene. According to this technology, it is possible to produce a nearly monodisperse random living copolymer of ethylene and propylene. This copolymer is reacted with a halogen to convert it into a copolymer having halogenated terminals. The copolymer is then reacted with a terminal converting agent to form the terminal carbocation of the copolymer. Finally, tetrahydrofuran is polymerized in the presence of the cation. Thus there is obtained a block copolymer of uniform composition which is composed of the segments of nearly monodisperse ethylene-propylene random copolymer and the segments of nearly monodisperse polymer formed by ring opening polymerization of tetrahydrofuran. The present invention was completed based on this finding.
The gist of this invention resides in a block copolymer having a number-average molecular weight of about 1,000 to about 1,000,000 in which the random copolymer segment (A) is bonded to the polymer segment (B), with the ratio of (A) to (B) being 5/95 to 95/5 by weight, said random copolymer segment (A) being composed of the constitutional units represented by the formulas I and II below, ##STR1## [the amount of I being 30 to 80 wt% and the amount of II being 70 to 20 wt%], and said polymer segment (B) being composed of the constitutional units represented by the formula --O.(CH.sub.2).sub.4 --. Said copolymer is produced by the steps of performing living polymerization of ethylene and propylene in the presence of .beta.-diketone vanadium chelate and an organoaluminum compound to give a living ethylene-propylene random copolymer, reacting the random copolymer with a halogen to give an ethylene-propylene random copolymer having halogenated terminals, reacting the random copolymer with a terminal converting agent to give terminal carbocations of ethylene-propylene random copolymer, and finally polymerizing tetrahydrofuran in the presence of the terminal carbocations.
The living ethylene-propylene random copolymer is produced by copolymerizing ethylene and propylene in the presence of a polymerization catalyst composed of .beta.-diketone vanadium chelate (referred to as vanadium compound hereinafter) and an organoaluminum compound.
The vanadium compound is represented by the formula below. ##STR2## (where R.sup.1 and R.sup.2 are the same or different alkyl groups or aryl groups.) It includes, for example, V(acetylacetonate).sub.3, V(benzoylacetylacetonate).sub.3, and V(dibenzoylmethanate).sub.3.
The organoaluminum compound is represented by the formula R.sub.2 AlX (where R is an alkyl group or aryl group having 1 to 8 carbon atoms, and X is a halogen atom). It includes, for example, dimethylaluminum chloride, diethylaluminum chloride, diethylaluminum bromide, and diisobutylaluminum chloride.
The polymerization reaction should preferably be performed in a solvent which is inert and liquid at the time of polymerization. Examples of the solvent include saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; saturated alicyclic hydrocarbons such as cyclopropane and cyclohexane; and aromatic hydrocarbons such as benzene, toluene, and xylene.
Ethylene and propylene can be brought into contact with the polymerization catalyst in any manner. Preferably, the contact is accomplished by adding a solution of the organo-aluminum compound and then a solution of the vanadium compound to a solvent solution of ethylene and propylene.
The amounts of the polymerization catalyst used for 1 mol of ethylene and propylene are as follows: The amount of the vanadium compound is 1.times.10.sup.-4 to 0.01 mol, preferably 5.times.10.sup.-4 to 5.times.10.sup.-3 mol, and the amount of the organoaluminum compound is 1.times.10.sup.-3 to 0.1 mol, preferably 5.times.10.sup.-3 to 0.01 mol. Preferably, the organoaluminum compound is used in an amount of 5 to 25 mol for 1 mol of the vanadium compound.
The molecular weight and yields of the living copolymer can be regulated by changing the reaction temperature and reaction time. According to this invention, it is possible to produce a polymer which has a molecular weight distribution similar to that of a monodisperse polymer, if the polymerization temperature is kept low, particularly lower than -50.degree. C. Polymerization at -65.degree. C. or below provides a living ethylene-propylene random copolymer having a molecular weight distribution of 1.05 to 1.40 which is defined by Mw/Mn (where Mw is the weight-average molecular weight and Mn is the number-average molecular weight.
The polymerization reaction may be accompanied by a reaction accelerator such as anisole, water, oxygen, alcohol (methanol, ethanol, isopropanol, etc.), and ester (ethyl benzoate, ethyl acetate, etc.). The reaction accelerator is used in an amount of 0.1 to 2 mol for 1 mol of the vanadium compound.
The ratio of ethylene to propylene in the living copolymer should be in such a range that the property of the final block copolymer attributable to the ethylene-propylene random copolymer in it is not adversely affected. The ethylene-to-propylene ratio is usually 30/70 to 80/20 by weight.
The composition of the ethylene-propylene random copolymer can be regulated by changing the ratio of ethylene to propylene at the time of living copolymerization. The greater the amount of ethylene used, the broader the molecular weight distribution of the resulting polymer, and this is not preferable. A living copolymer of high ethylene content having a narrow molecular weight distribution (or a nearly monodisperse living copolymer) can be produced by performing living polymerization of a small amount of propylene prior to the living copolymerization of ethylene and propylene. The living copolymer obtained in this way has a narrow molecular weight distribution and yet contains a large amount of ethylene. In actual, propylene alone is supplied at first to the polymerization system so that living polypropylene having a number-average molecular weight of 500 to 2000 is formed. Subsequently, ethylene is supplied to continue living polymerization in the presence of a large amount of unreacted propylene monomer until the random copolymerization of ethylene and propylene is completed.
In the way mentioned above, it is possible to produce a nearly monodisperse living ethylene-propylene random copolymer having a number-average molecular weight of about 500 to about 500,000 (in terms of propylene, to be repeated hereinafter).
In the next step, the random copolymer is brought into contact with a halogen so that the polymerization of ethylene and propylene is suspended immediately. The resulting product is an end-halogenated ethylene-propylene random copolymer having the skeleton of the above-mentioned living copolymer.
The halogen that can be used in that step is iodine, chlorine, or bromine, and it is used in an amount of 2 mol and up, preferably 2 to 5 mol, for 1 mol of the organoaluminum compound used. The halogen may be used as such; but it should preferably be used in the form of solution in the same solvent as used for the above-mentioned living copolymerization. The concentration of the solution is 0.1 to 5 mol in 1 liter of the solvent. Usually, halogenation is performed for 5 minutes to 6 hours at -50.degree. to -100.degree. C.
Upon addition of an alcohol to the reaction system, the halogenated ethylene-propylene random copolymer separates out.
The halogenated ethylene-propylene random copolymer thus obtained is then reacted with a terminal converting agent represented by the formula MY (where M denotes Ag, Na, Li, K, Rb, or Cs; and Y denotes ClO.sub.4, BF.sub.4, PF.sub.6, AsF.sub.6, or SbF.sub.6). Examples of this agent include AgClO.sub.4, AgBF.sub.4, KClO.sub.4, LiClO.sub.4, AgSbF.sub.6, AgPF.sub.6, AgAsF.sub.6, NaSbF.sub.6, KSbF.sub.6, LiSbF.sub.6, NaPF.sub.6, KPF.sub.6, LiPF.sub.6, NaAsF.sub.6, KAsF.sub.6, LiAsF.sub.6, NaBF.sub.4, KBF.sub.4, and LiBF.sub.4.
The terminal converting agent is used in an amount of 1 mol or up, preferably 1.5 to 30 mol, for 1 mol of the halogenated ethylene-propylene random copolymer. The reaction between the halogenated copolymer and the terminal converting agent is usually performed in a solvent. The same solvent as used for the above-mentioned living polymerization can be used for this purpose, and tetrahydrofuran may also be used as well.
The above-mentioned reaction forms the terminal carbocation of ethylene-propylene random copolymer. This cation serves as an initiator for the polymerization of tetrahydrofuran (abbreviated as THF hereinafter). As the result of the polymerization of THF, there is obtained the block copolymer of this invention.
The terminal conversion reaction of the halogenated ethylene-propylene random copolymer and the subsequent polymerization of THF are performed at -80.degree. C. to +50.degree. C., preferably -20.degree. C. to +20.degree. C., for 3 hours or longer, preferably 5 hours or longer. The polymer segment (B) formed by the ring opening polymerization of THF increases in molecular weight as the polymerization temperature for THF is raised or the polymerization time for THF is extended.
THF is used in an amount of 10 times (by weight), preferably 20 times, the amount of the halogenated copolymer.
The polymerization reaction of THF can be suspended by adding an alcohol such as methanol and ethanol to the polymerization system. After polymerization, excess THF is removed and the precipitated solids are washed with acetone, methanol, or the like and dried. In this way, the block copolymer is recovered.
Thus there is obtained an AB-type block copolymer in which the copolymer segment (A) formed by random copolymerization of ethylene and propylene is connected to the polymer segment (B) formed by ring opening polymerization of THF. This copolymer has a number-average molecular weight of about 1,000 to about 1,000,000, preferably 3,000 to 300,000, more preferably 5,000 to 200,000. The ratio of segment (A) to segment (B) in the copolymer is 5/95 to 95/5 (by weight).
The molecular weight and composition of the block copolymer can be regulated by changing the molecular weight and composition of the living ethylene-propylene random copolymer and the conditions for polymerization of THF.
The block copolymer of this invention is characterized by that it is a nearly monodisperse polymer of uniform composition having a molecular weight distribution (Mw/Mn) of 1.05 to 1.40.
The block copolymer of this invention is composed of nonpolar polymer segments (A) and polar polymer segments (B). Therefore, it differs in properties from the conventional block copolymers and polymer mixtures. It is useful as a dyeing agent, adhesive, polymer modifier, compatibilizing agent, and surface modifier.